With rapid development of machine-to-machine (M2M) communications applications, a market requirement and scale are growing explosively. An M2M communications application has a service requirement different from that of a conventional communication service, such as deep coverage and low power consumption. A propagation latency exists in signal propagation. For example, in uplink transmission of a communications system, a signal sent by a terminal device to a base station at a moment 1 may be received by the base station at a moment 2 because a propagation latency exists in signal propagation. Therefore, before communicating with the base station, the terminal device needs to send a segment of training signal, so that the base station can estimate a latency of propagation between the base station and the terminal device, and then notify the terminal device of the latency. In this way, the terminal device can correspondingly send uplink data in advance based on the latency.
A current solution is as follows: In a Long Term Evolution (LTE) system, the terminal device simultaneously sends a random access channel (RACH) signal on 839 subcarriers, so that the base station estimates a propagation latency based on the received RACH signal.
A larger quantity of subcarriers occupied by a signal indicates a higher peak-to-average power ratio (PAPR) of the signal. In the foregoing solution, the RACH signal occupies 839 subcarriers of transmission bandwidth. Therefore, a PAPR in the foregoing solution can be excessively high. The excessively high PAPR reduces power amplifier efficiency of the terminal device, and consequently the terminal device needs quite high transmit power, causing an increase of power consumption of the terminal device.